When we were first working on things because there was the need to rebuild trust, it was understood that everything was allowed to be read. Now I wasn't actively with anyone so it was just messages to friends and things like that and that was established. Now that was something we knew though, there was not the secret reading of information.
That was also an attempt to reestablish trust that had already been broken. The 'rules' now are different. While BF knows that our chats are often read, kids over shoulder, me out loud to hubby certain things and kids and him exchanging greetings, if someone sits close or is glancing and we want privacy we ask for it. Mostly our chats are daily catch ups and stuff and do become a larger affair as we tease and talk amongst ourselves. (Also, I was stuck typing the 'dibs war' over fantasy weapons at one point while the two guys kept swearing and trying to one up each other.)
I think the part that is getting people is where one person's boundaries are being set for everyone else. Not even discussed just, this is what I want and so this is how it goes. That doesn't fly long in ANY relationship.
Me: Late 30s pansexual poly.
DH: My husband of 19 yrs and father of 3 teen girls.
DC: LDR of +4 year